1. Field of the Invention
This invention relates to a new process for the production of light-resistant, optionally foamed, elastomeric molded polyurethanes by the reaction of organic polyisocyanates inside closed molds with compounds containing at least two isocyanate reactive groups in the presence of catalysts, wherein the polyisocyanates used are based on certain mixtures of selected polyisocyanates containing aliphatically or cycloaliphatically bound isocyanate groups.
2. Description of the Prior Art
The production of light-resistant elastic polyurethane foams from aliphatic and/or cycloaliphatic polyisocyanates is known, but it has previously been necessary to use very special catalyst combinations for the production of such foams because aliphatic and cycloaliphatic polyisocyanates are much less reactive than the aromatic polyisocyanates conventionally used for the production of polyurethane foams.
In DE-OS 3,008,811, for example, it is recommended to catalyze the reaction for the formation of polyurethanes by means of compounds containing primary or secondary amino groups in combination with an organic bismuth compound.
In DE-OS No. 2,447,067 and DE-OS No. 2,710,901, special combinations of certain amines, amidines or guanidines with alkaline earth metal salts and combinations of compounds containing primary or secondary amino groups with lead compounds are recommended.
The combination of alkali metal compounds and/or hexahydrotriazine derivatives with organic tin, zinc and/or iron(II) compounds is recommended in DE-OS No. 2,825,569.
Finally, DE-OS No. 2,832,253 recommends the use of alkali metal hydroxides and alkaline earth metal hydroxides in combination with organic tin, lead and iron compounds.
The process according to the invention described below discloses a new method of preparing light-resistant, elastic molded polyurethane parts in which polyisocyanates are reacted with components containing isocyanate reactive groups and auxiliary agents to give rise to high quality end products. The process according to the invention described in detail below is characterized by the use of mixtures of IPDI with polyisocyanates containing isocyanurate groups, in particular those based on 1,6-diisocyanatohexane, and in this respect it differs from the process described in the present Applicants' earlier German Patent Application No. P 3,527,863.3. The process according to the invention described below in particular results in molded products which have a pleasant, dry feel.